Referring to FIG. 6, there is shown a fixing structure of this kind in section. A fork stem 1 is coupled at its upper end with a handlebar stem in a head pipe (not shown). A lower end of the fork stem 1 is inserted into a fork shoulder 2 and is brazed thereto with hard solder 3. Each upper end of a pair of fork legs 4 is inserted into the fork shoulder 2 and is brazed thereto with hard solder 3'.
In the fixing structure of in FIG. 6, brass is generally used as the hard solder 3(3') while the brazing with the hard solder 3 cannot join different metal materials. Accordingly, since the fork stem 1 formed of, for example, chromium molybdenum steel and the fork shoulder 2 formed of, for example, an alloy of aluminum can not be brazed with hard solder 3, other joining means must be adopted. Further, the brazing with hard solder 3 requires skill and time and since the fork shoulder 2 is heated to a high temperature of about 900.degree. C. and is softened, the mechanical strength thereof is deteriorated.
Recently, various methods of joining the fork stem and the fork shoulder formed of different metal materials have been proposed. For example, Japanese Utility Model Unexamined Publication No. 62-115288 discloses a structure of joining a fork stem and a fork shoulder formed of different metal materials in which a lower end of the fork stem is inserted into a sleeve to join the fork stem and the sleeve with adhesive and the sleeve is then fitted into the fork shoulder to be welded together. However, since this structure requires the sleeve and thread grooves formed on the lower portion of the fork stem and the sleeve, it requires high material and work cost and is therefore expensive.
Further, Japanese Utility Model Unexamined Publication No. 62-189295 also discloses a structure in which a lower portion of a fork stem is directly screwed into a hole formed in a fork shoulder and both of them are joined with adhesive. This structure can reduce the number of parts, through it requires work for forming thread grooves and high labor cost.
In addition, Japanese Utility Model Unexamined Publication No. 58-111687 discloses a structure in which a cylindrical portion is integrally provided in a fork shoulder and a tapered portion in a lower portion of a fork stem is fitted into a tapered hole formed in the cylindrical portion so that both the fork shoulder and fork stem are fixed with adhesive. This is advantageous in that the number of parts is small, labor for forming a thread groove and effecting welding are not required and furthermore assembling work is easy. However, since only the adhesive is used, the joining strength is deteriorated.